Electrical connection with inwardly deformable contacts

ABSTRACT

An interposer for interconnection between microelectronic circuit panels has contacts at its surfaces. Each contact extends from a central conductor, and has a peripheral portion adapted to contract radially inwardly toward the central conductor response to a force applied by a contact pad defining a central hole on the engaged circuit panel. Thus, when the circuit panels are compressed with the interposers, the contacts contract radially inwardly and wipe across the pads. The wiping action facilitates bonding of the contacts to the pads, as by friction welding, or by a conductive bonding material carried on the contacts themselves.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of patent application Ser.No. 08/989,305, filed Dec. 12, 1997, which claims the benefit ofProvisional Patent Application No. 60/032,884, filed Dec. 13, 1996,which applications are hereby incorporated by reference in theirentirety herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to the field of electricalcircuitry, and more particularly relates to layered circuit structuressuch as multilayer circuit boards, to components and methods utilized infabrication of such structures and to methods of making the same.

[0003] Electrical components are commonly mounted on circuit panelstructures such as printed circuit boards. Circuit panels ordinarilyinclude a generally flat sheet of dielectric material with electricalconductors disposed on a major, flat surface of the sheet or on bothmajor surfaces. The conductors are commonly formed from metallicmaterials such as copper and serve to interconnect the electricalcomponents mounted to the board. Where the conductors are disposed onboth major surfaces of the panel, the panel may have via conductorsextending through the dielectric layer so as to interconnect theconductors on opposite surfaces. Multilayer circuit panel assemblieshave been made heretofore which incorporate plural, stacked circuitpanels with additional layers of dielectric materials separating theconductors on mutually facing surfaces of adjacent panels in the stack.These multilayer assemblies ordinarily incorporate interconnectionsextending between the conductors on the various circuit panels in thestack as necessary to provide the required electrical interconnections.

[0004] Electrical components which can be mounted to circuit panelstructures include so-called “discrete” components and integratedcircuits which include numerous transistors on a single chip. Chips ofthis nature can be mounted to elements commonly referred to as “chipcarriers” which are specialized circuit panel structures. A chip carriermay be incorporated in a package which is mounted to a larger circuitboard and interconnected with the remaining elements of the circuit.Alternatively, the chip can be mounted directly to the same circuitpanel which carries other components of the system. This arrangement isordinarily referred to as a “hybrid circuit”. Relatively large circuitpanels are commonly made of polymeric materials, typically withreinforcement such as glass, whereas very small circuit panels such asthose used as semiconductor chip carriers may be formed from ceramics,silicon or the like.

[0005] There have been increasing needs for circuit panel structureswhich provide high density, complex interconnections. These needs areaddressed by multilayer circuit panel structures. The methods generallyused to fabricate multilayer panel structures have certain seriousdrawbacks. Multilayer panels are commonly made by providing individual,dual sided circuit panels with appropriate conductors thereon. Thepanels are then laminated one atop the other with one or more layers ofuncured or partially cured dielectric material, commonly referred to as“prepregs” disposed between each pair of adjacent panels. Such a stackordinarily is cured under heat and pressure to form a unitary mass.After curing, holes are drilled through the stack at locations whereelectrical connections between different boards are desired. Theresulting holes are then coated or filled with electrically conductivematerials, typically by plating the interiors of the holes to form whatis called a plated through hole.

[0006] It is difficult to drill holes with a high ratio of depth todiameter. Thus, the holes used in assemblies fabricated according tothese prior methods must be relatively large and hence consumesubstantial amounts of space in the assembly. These holes ordinarilyextend from the top or bottom of the stack. Even where interconnectionsare not required in the top or bottom layers, space must be provided forholes to pass through these layers so as to provide neededinterconnections in the middle layers. Accordingly, substantial amountsof the available surface area on the panels must be allocated to theholes and to accommodate tolerance zones around the holes. Moreover, theelectrical interconnections formed by depositing conductive materials insuch drilled holes tend to be weak. The drilling method and the generalnature of the laminates used therein is described, for example inDoherty, Jr., U.S. Pat. No. 3,793,469; and Guarracini, U.S. Pat. No.3,316,618.

[0007] Various alternative approaches have been proposed. Parks, et al.,U.S. Pat. No. 3,541,222; Crepeau, U.S. Pat. No. 4,249,032; Luttmer, U.S.Pat. No. 3,795,037; Davies, et al., U.S. Pat. No. 3,862,790, Fox, U.S.Pat. No. 4,954,878, and Zifcak, U.S. Pat. No. 4,793,814 all relategenerally to structures which have metallic or other conductive elementsarranged at relatively closely spaced locations on a dielectric sheetwith the conductive elements protruding through the dielectric sheet inboth directions. Such a sheet may be sandwiched between a pair ofcircuit boards and the circuit boards may be clamped or otherwise heldtogether so as to provide mechanical engagement between conductiveelements on the adjacent faces of the circuit boards and the conductiveelements of the composite sheet. In each of these arrangements, theconductive elements, the composite sheet or both is resilient ormalleable so as to provide for close engagement between the conductiveelements of the composite sheet and the conductors on the circuitboards.

[0008] Beck, U.S. Pat. No. 3,616,532 and Dube, et al., U.S. Pat. No.3,509,270 describe variants of this approach in which resilient elementsare used with a fusible solder. These elements are mounted on insulatingboards which are then stacked between printed circuit layers. Theassembly is heated so as to melt the solder, thereby freeing theresilient elements so that the resilient elements and soldercooperatively form an interconnection between the adjacent circuitboards.

[0009] Evans, et al, U.S. Pat. No. 4,655,519 describes a connector withnumerous strip-like contact springs disposed in holes in a flatdielectric body, together with other spring elements. The ends of thestrips protrude from opposite surfaces of the body. These are adapted tocompress when electronic elements are engaged with the body surfaces, sothat the ends of the strips engage pads on the electronic elements.Walkup, U.S. Pat. No. 5,167,512 discloses a further system using springsdisposed in holes in a dielectric body.

[0010] Grabbe, U.S. Pat. No. 5,228,861 describes a connector having asheet-like dielectric body with numerous generally X-shaped springcontact elements, each having four arms, lying on a first side of thesheet. Two arms of each X-shaped element are bent inwardly toward thesheet, and extend through holes in the sheet so that the tips of thesearms protrude above the second, opposite face of the sheet. The othertwo arms are bent away from the sheet, and hence protrude from the firstsurface. When the connector is placed between circuit panels, eachX-shaped element is compressed between mating pads of the circuitpanels, causing the bent arms to flatten and causing the tips of thearms to wipe the surfaces of the pads. After engagement, the contact ismaintained by the resilience of the arms.

[0011] Bernarr, et al., U.S. Pat. No. 4,548,451 describes a connector orinterposer having a sheet-like elastomeric body with crushableprotrusions extending outwardly from oppositely-directed surfaces. Tabsformed from a metal-coated flexible film extend on both surfaces of thebody, and overlie the protrusions. The tabs on opposite sides areconnected to one another by vias. When the interposer is engaged betweencircuit panels, the tabs and posts are crushed between contact pads onopposing panels, and the tabs assertedly wipe the pads for moreeffective contact. The tabs are maintained in engagement with the padsby the resilience of the elastomeric sheet and the posts; there is nopermanent bond formed.

[0012] Patraw, U.S. Pat. Nos. 4,716,049; 4,902,606; and 4,924,353describe microelectronic connection schemes using deformable contactsprotruding upwardly from a substrate. Each contact has a dome-like tipand a plurality of legs extending downwardly from the tip to thesubstrate. These contacts are formed by selective deposition of aluminumon pedestals of a fugitive material such as potassium chloride or aphotoresist using a shaped mask. The pedestals are removed afterdeposition.

[0013] Dery, et al., U.S. Pat. No. 4,729,809 discloses the use of ananisotropically conductive adhesive material disposed between opposingsublaminates, the adhesive composition having sufficient conductivityacross the relatively small spaces between conductors on adjacent layersto form an electrical interconnection therebetween, but having lowconductivity across the relatively large spaces between adjacentconductors on the same surface so that it does not produce an unwantedlateral interconnection along one surface.

[0014] Berger, et al., U.S. Pat. No. 4,788,766 uses conductor bearingcircuit lamina having hollow, eyelet-like via structures, each such viastructure having a rim protruding vertically from the surroundingstructure. Each such via structure is provided with a thin layer of aconductive bonding material. In making the multilayer structure,dielectric bonding films are interposed between the circuit bearinglamina. The dielectric films have apertures in locations correspondingto the locations of the eyelet structures, in the adjacent circuitbearing lamina. Thus, the upstanding rims of the eyelet structures canbear upon one another when the assembly is forced together under heatand pressure. The layers of conductive bonding material on the rims ofthe abutting eyelets are said to form bonds between the abutting eyeletstructures.

[0015] Co-pending U.S. patent application Ser. No. 08/277,366 of ThomasH. DiStefano, et al., which is assigned to the same assignee as thepresent application, discloses an interposer having deformable contactsprotruding upwardly from its surfaces. Each contact has a central axisnormal to the surface and a peripheral portion adapted to expandradially outwardly from the central axis in response to a force appliedby a pad on an engaged circuit panel. Thus, when the circuit panels arecompressed with the interposers, the contacts expand radially and wipeacross the pads. The wiping action facilitates bonding of the contactsto the pads, as by conductive bonding material carried on the contactsthemselves.

[0016] Other structures for forming multilayer electronic assemblies aretaught in Dux, et al., U.S. Pat. No. 5,224,265 and Ehrenberg, et al.,U.S. Pat. No. 5,232,548, which use sublaminates made by depositing adielectric material onto a perforated metal sheet, as by vapor-phasepolymerization or electrophoretic bonding, to form a dielectric sheetwith vias. The vias are filled with a flowable joining material such asa metal-loaded polymer. These structures are stacked and heated to jointhe vias into unitary vertical conductors.

[0017] Other multilayer assembly systems using flowable conductivematerials to join structures in stacked elements are disclosed inBindra, et al., U.S. Pat. No. 5,129,142. Still further improvements aredisclosed in U.S. Pat. No. 5,282,312 of Thomas H. DiStefano, et al. The'312 patent discloses as background certain lamination techniques ormethods of making multilayer circuit assemblies using flowableconductive materials.

[0018] Despite these and other efforts in the art, there are needs forstill further improvement.

SUMMARY OF THE INVENTION

[0019] The present invention addresses these needs.

[0020] One aspect of the present invention provides an interposer formaking connections to electrical contact pads on a surface of amicroelectronic element, such as a circuit panel, a semiconductor chipor other element having a contact bearing surface. The contacts defineholes therein. The interposer includes a body having a first majorsurface, such that the body has horizontal directions parallel to thefirst major surface and vertical directions perpendicular to the firstmajor surface. The interposer further has a plurality of conductors inthe body, such as via conductors extending in or through the body. Theinterposer further has a plurality of contacts on or above the firstmajor surface. Each of the contacts is permanently joined to one of theconductors, and extends radially outwardly from the conductor. Thus,each contact extends in a plurality of horizontal directions away fromthe conductor. Each contact has a periphery remote from the conductorand a central portion attached to the conductor. The contacts areadapted to deform so that the periphery of the contact will contractradially inwardly toward the central portion of the contact in responseto urging the periphery of the contact against one of the contact padson the surface of the microelectronic element, and inserting the centralportion of the contact into the hole defined by the contact pad. As themicroelectronic element is juxtaposed with the first surface of theinterposer and forced toward the body, the contacts will wipe thecontact pads of the microelectronic element. The wiping action removesoxides and other contaminants from the mating surfaces to provide aneffective, low resistance electrical connection between the pads and thecontacts and, in preferred embodiments, to facilitate bonding of thecontacts and the pads.

[0021] The contacts are desirably arranged to deform so that the contactbends vertically downward, with the periphery of the contact movingtoward the body, as well as contracting radially inwardly toward thecentral portion of the contact. In the initial, undeformed condition,the periphery of each contact may be spaced vertically above the body,with a gap between the periphery of the contact and the body. The bodymay be deformable at least near the periphery of each of the contacts,such that movement of the periphery downwardly causes the periphery toengage and deform the body. The body may have an adhesive layer coveringthe first major surface for adhering the interposer to themicroelectronic element upon juxtaposition of the two components. Thecontacts may be disposed on the adhesive layer, and the adhesive layermay have a thickness beneath the contacts greater than the thickness ofthe adhesive layer between the contacts. Such a configuration supportsthe contacts during handling, while maintaining the contact in anextended position for assuring contact with contact pads on an adjacentmicroelectronic element.

[0022] The periphery of each of the contacts may be noncircular. Forexample, each of the contacts may include a plurality of tabs extendingradially outwardly from the conductor, with each of the tabs having atip remote from the conductor. The tabs of each contact may be disposedin a substantially symmetrical pattern about the juncture of the contactand the associated conductor. The contact may include four such tabs, inwhich case the substantially symmetrical pattern in a quatrefoilpattern. The contacts may be disposed in a substantially rectilineargrid having rows and columns, the individual tabs extendingsubstantially diagonally with respect to the row and columns. Thediagonal tabs permit a maximum contact density for a given tab size. Thecontacts may take other forms. For example, the tabs may be disposed ina star pattern with the tips of the tabs having a circumferential widthless than a circumferential width of the tabs near the central portion.In this case, the tips may be pointed so as to enhance wiping betweenthe contacts and the contact pads. Alternatively, the circumferentialwidth of the tabs near the tips may be greater than the circumferentialwidth near the central portion. Such a configuration promotes wipingalong the edges of the contacts.

[0023] The contact may include a conductive bonding material adapted tofacilitate electrical joining of the tabs to contact pads engaged withthe tabs. The conductive bonding material may be selected from the groupconsisting of solders, brazing alloys, defusion bonding alloys andconductive materials incorporating a polymer.

[0024] The contact may be formed integrally with an associatedconductor. The conductor may extend substantially perpendicularly to thefirst surface of the body. The conductors may be arranged in the body ata pitch of less than about 1 mm from center to center. The pitch maytherefore be chosen to correspond to standard pitches used in presentand future microelectronic element contact arrays.

[0025] The interposer may be two-sided. In that case, the body defines asecond major surface facing in an opposite direction from the firstmajor surface. At least some of the conductors are through conductorshaving first ends disposed adjacent to the first major surface andsecond ends disposed adjacent to the second major surface. At least someof the contacts are permanently joined to the first ends of the throughconductors. Second end contacts are provided on or above the secondmajor surface of the body, and are permanently joined to the second endsof the conductors. Each of the second end contacts extends radiallyoutwardly from the associated conductor, and has a periphery remote fromthe conductor. Each of the second end contacts is adapted to deform sothat the periphery of the contact will contract radially inwardly towardthe central portion of the contact in response to engaging a secondmicroelectronic element. The element is engaged by urging a periphery ofthe contact against a contact pad of the second microelectronic elementand inserting the central portion of the contact into a hole defined bythe contact pad. Upon engagement, the contacts wipe the contact pads ofthe second microelectronic element when the second microelectronicelement is juxtaposed with the second surface and forced toward thebody.

[0026] In another embodiment of the invention, an interposer is providedfor making connections to a microelectronic element having pads definingholes therein. The interposer includes an interposer body having a firstsurface and a plurality of contacts on the body. Each of the contactshas a central portion extending through the first surface into the body,and a peripheral portion extending radially from the central portion onor above the first surface. The peripheral portion of each contact isadapted to bend downward toward the body. The central portion is adaptedto remain substantially undeformed in response to a force on theperipheral portion directed downward toward the body.

[0027] The central portions of the contacts may be substantiallycylindrical. The peripheral portions may include a plurality of tabsextending radially from the central portion. The interposer may furtherinclude a deformable layer between the first surface and the peripheralportions of the contacts to allow the peripheral portions to benddownward into the deformable layer upon engagement with the contact padson the microelectronic element. The deformable layer supports thecontacts during transport, while permitting them to deflect uponengagement. The deformable layer may be an adhesive layer. Theperipheral portion of the contact may be spaced apart from the body,defining a gap therebetween.

[0028] In another embodiment of the invention, an interposer for makingconnections to electrical contact pads on a surface of a microelectronicelement is provided. The interposer includes an interposer body have afirst surface and a plurality of contacts on the body. Each of thecontacts includes a central portion and a plurality of tabs extendingradially outward from the central portion. Each of the tabs extends overthe first surface, and is adapted to deform radially inward toward thecentral portion of the contact, in response to a force on the tabdirected downward toward the body. The tabs may have asperities on topsurfaces facing upward away from the body. The asperities engage andwipe a contact pad engaged with the contact, breaking through anyoxidation that may be present on the contact pad in order to form a morereliable electrical contact.

[0029] In a method for making a multilayer circuit according to thepresent invention, a circuit panel and an interposer are stacked so thata first surface of the interposer confronts a surface of the panel. Theinterposer has a body defining the first surface, and conductors havingends adjacent or above the first surface. The interposer further hascontacts on the conductor ends, including peripheral portions extendinggenerally horizontally from the associated conductor ends. Theperipheral portions of the contacts confront contact pads on the circuitpanel. The contact pads on the circuit panel define holes facing theinterposer.

[0030] The method further comprises the step of compressing the stackedpanel and the interposer together. In this step, conductor ends enterthe holes in the circuit panel, while the peripheral portions of thecontacts are forcibly engaged with the contact pads. This causes theperipheral portion of each contact to be contracted radially inwardtoward the associated conductor end so that each peripheral portionmoves horizontally with respect to the engaged contact pad, and wipesthe contact pad.

[0031] The conductor ends in the interposer used in the method have avertical position with respect to the first surface of the interposer.That vertical position remains substantially unchanged during thecompressing step. Further, the compressing step may be performed so thatthe peripheral portion wipes the contact pad at an edge of the contactpad defining the hole. In that case, the peripheral portion may comprisea plurality of tabs extending radially outward from the conductor. Thetabs have edges extending in a substantially radial direction, the edgesof the tabs wiping the edges of the holes during engagement.

[0032] The holes in the contact pads used in the method may be circularor may alternatively be polygonal, in which case they are defined by aplurality of edges wherein adjacent ones of the edges form a pluralityof vertices. Where the holes are polygonal, the peripheral portion of anadjoining contact may form a circular outer edge having a diameterlarger than a minimum diameter of the polygonal hole. The circular outeredge wipes the edges defining the polygonal hole. The peripheral portionof the contact may alternatively have a plurality of tabs, each of thetabs corresponding to a single vertice of the polygonal hole. The tabsare aligned with the vertices so that during the compressing step, eachtab wipes two adjacent edges of the hole.

[0033] The contact pad may be connected to a conductive via formed inthe hole defined by the contact pad. During the compressing step, theperipheral portion of the contact may move vertically downward towardthe body of the interposer.

[0034] The stacking step of the above-described method may furtherinclude the step of stacking a plurality of circuit panels and at leastone interposer, in an interweaved, vertically alternating arrangement.In such an arrangement, an interposer is disposed between each pair ofcircuit panels, with oppositely-directed first and second horizontalsurfaces of each of the interposers confronting surfaces of the panels.The conductors of each of the interposers include through conductorsextending through the body of the interposer and having their ends andcontacts at or above first and second surfaces of the interposer. Thecontact pads on the plurality of panels are interconnected with oneanother by the through conductors.

[0035] The method may also include the step of bonding the contacts tothe contact pads. The bonding step may include momentarily heating thestacked panels and interposers to activate electrically conductivebonding material that interfaces between the contacts and the vias. Thebonding material may be carried on the contact pads. The momentaryheating step may cause a softening of the body of the interposer,thereby facilitating vertical movement of the peripheral portions of thecontacts during the compressing step.

[0036] The method may include the step of causing an adhesive such as adielectric bonding material to flow at interfaces between theinterposers and the panels during the compressing step so as to fuse theinterposer and the panel into a substantially unitary mass. The step ofcausing the dielectric bonding material to flow may include momentarilyheating the stacked panels and interposers.

[0037] Each contact of the interposer used in the method may include aplurality of tabs extending generally radially outward in asubstantially symmetrical pattern from the associated conductor end.During the compressing step, each tab is bent so that a tip of each tabremote from the conductor moves downwardly toward the interposer bodyand horizontally toward the conductor end. All the tabs in each of thecontacts may be engaged with the same contact pad during the stackingstep.

[0038] In the method of the invention, the first surface of theinterposer may be coated with an adhesive such as a pressure-sensitiveadhesive. The adhesive is activated during the compressing step to bondthe first surface of the interposer to the surface of the panel.Further, wiping of the peripheral portions of the contacts on thecontact pads may cause at least some of the peripheral portions to befriction welded to corresponding ones of the contact pads.

[0039] In a method of making a circuit assembly according to anotheraspect of the invention, a circuit panel and an interposer are stackedin a vertically superposed arrangement so that a first horizontallyextensive surface of the interposer confronts a first horizontallyextensive surface of the circuit panel. A plurality of electricallyconductive contacts on the first surface of the interposer confrontscontact pads on the circuit panel. The contact pads face the interposerand define holes in the contact pads. The stacked panel and interposerare then pressed vertically so as to forcibly engage the contacts withthe contact pads. The contacts are caused to deform so that at least aportion of each contact enters a hole defined by one of the contact padsand at least a portion of each contact engages the contact pad and moveshorizontally inward and vertically downward with respect to the firstsurface of the interposer, thereby wiping the contact pad. The contactsmay wipe the contact pads at edges defining the holes.

[0040] This process of the invention may further include the step ofbonding each contact to the engaged contact pad. The bonding step mayinclude the step of activating bonding material at interfaces betweenthe contacts and the vias by momentarily heating the stacked interposerand circuit panel. The bonding material may be present on the contacts,the contact pads or both prior to the stacking step.

[0041] The interposer in this method may include a dielectric layer atthe horizontally-extensive surface. The contact in that case includes aportion in contact with the dielectric layer and bearing on the engagedcontact pad during the compressing step. The momentary heating softensthe dielectric layer to facilitate vertical downward deformation of thecontacts. The bonding may alternatively or additionally includecompressing the stacked panel and the interposer so that portions of thecontacts wipe the contact pads with sufficient force to friction weldthe contacts to the engaged contact pads.

[0042] In a method of making a microelectronic interposer according tothe invention, a body is provided having a first surface. A temporarylayer is provided over the first surface of the body. Apertures passingthrough the body and the temporary layer are formed, and a layer of anelectrically conductive structural material is deposited in each of theapertures and over the temporary layer proximate the aperture. Theconductive structural material forms contacts on the temporary layerthat extend into the apertures. The temporary layer is then removed,leaving the contacts with outwardly flaring peripheral portions that arespaced vertically above the first surface of the body.

[0043] An adhesive may be deposited on the first surface of the bodybefore providing the first temporary layer. The temporary layer is thenprovided over the adhesive layer, and the adhesive layer is left exposedafter the temporary layer is removed. The adhesive layer may be athermoplastic or b-staged adhesive. In a preferred embodiment, theadhesive may be a material selected from the group of polyimide andpolyetherimide (PEI). The temporary layer may be formed from a metalselected from a group consisting of aluminum, tin and nickel.

[0044] The body may also define a second surface opposite the firstsurface. In that case, the method further comprises providing a secondtemporary layer over the second surface, with the apertures passingthrough the second temporary layer, as well as the first temporary layerand the body. The electrically conductive structural material isdeposited so as to extend over the second temporary layer proximate theapertures to thereby form second contacts.

[0045] In another method of making a microelectronic interposeraccording to the invention, a body defining the first surface isprovided, and a first compliant layer is formed over the first surface.Apertures are then formed passing through the body and the compliantlayer. A layer of an electrically conductive structural material is thendeposited in each of the apertures and over the compliant layerproximate the aperture to form contacts with outwardly flaringperipheral portions on the compliant layer. The compliant layer may bean adhesive. The compliant layer may be partially etched so that thecompliant layer has a thickness under the contacts greater than athickness between the contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a fragmentary, diagrammatic perspective view depictingan interposer according to one embodiment of the invention;

[0047]FIG. 2 is a fragmentary, diagrammatic sectional view taken throughline II-II of FIG. 1 depicting an interposer according to one embodimentof the invention, together with two partial circuit panels forengagement therewith;

[0048]FIG. 3 is a fragmentary, diagrammatic sectional view of theinterposer and circuit panels of FIG. 2 after engagement;

[0049]FIG. 4 is a diagrammatic, perspective view depicting an interposeraccording to one embodiment of the invention;

[0050]FIG. 5 is a fragmentary, diagrammatic sectional view of a contactof the interposer of FIG. 4, taken through line V-V;

[0051]FIG. 6 is a diagrammatic, sectional, perspective view of a contactand associated portion of an interposer according to one embodiment ofthe invention;

[0052]FIG. 7 is a diagrammatic, sectional, perspective view of a contactand associated portion of an interposer according to one embodiment ofthe invention, engaged with a corresponding contact pad of a circuitpanel;

[0053] FIGS. 8-10 are a diagrammatic, sectional, perspective views ofcontacts and associated portions of interposers according to variousembodiments of the invention;

[0054]FIG. 11 is a schematic plan view of a contact of an interposeraccording to the invention, showing its size relative to a hole of amating contact pad of a circuit panel;

[0055]FIG. 12 is a schematic plan view of a contact of an interposeraccording to the invention, showing its relative location with respectto a hole of a mating contact pad of a circuit panel;

[0056] FIGS. 13A-13C are schematic plan views, respectively, of acontact pad on a circuit panel, a corresponding contact on an interposerand the contact and contact pad in a superposed position, according tothe invention;

[0057]FIG. 14 is a schematic plan view of a contact of an interposeraccording to another embodiment of the invention shown superposed over ahole of a contact pad;

[0058]FIG. 15 is a schematic plan view of a contact of an interposeraccording to another embodiment of the invention shown superposed over ahole of a contact pad;

[0059] FIGS. 16A-16J are schematic plan views of contacts of interposersaccording to various embodiments of the invention, shown together withcorresponding contact pads of circuit panels; and

[0060] FIGS. 17A-17E are fragmentary, diagrammatic, sectional viewsdepicting a portion of an interposer during various stages of afabrication process according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] An interposer according to one embodiment of the invention, shownin FIG. 1, has a body 60 with a first major surface 65. The body 60 maybe formed of a dielectric material such as polyimide, or of anothernon-conducting material. The top surface 65 of the body 60 extends inhorizontal directions; i.e., directions x, y as shown in FIG. 1. Aplurality of conductors 72 extend vertically, or in the z direction,into the body. In the preferred embodiment shown in FIG. 1, theconductors 72 extend through the body 60. The conductors 72 may beelements formed by conductively plating vertical holes extending intothe body 60 from the first surface 65. The conductors are formed of astructural conductive material such as copper, gold, tin or alloysthereof.

[0062] Each of the conductors 72 has a first end 71 positioned on orabove the first major surface 65 of the body 60. Extending radiallyoutward from the end 71 of the conductor is a contact 70. In thepreferred embodiment shown in FIG. 1, the contact 70 comprises foursubstantially evenly spaced tabs 73. The contact 70 includes a peripheryor peripheral portion 74 remote from the conductor, and a centralportion 75 attached to the conductor 72.

[0063] A compliant layer 62 is formed on the first major surface 65 ofthe body, and lies between the body and the contacts 70. The compliantlayer 62 is preferably an adhesive, such as a thermoplastic adhesive foradhering to a mating circuit panel as described below. The contacts 70may rest directly on a top surface 63 of the compliant layer 62, or maybe positioned above the top surface 63.

[0064] As best shown in FIGS. 1 and 2, the interposer body 60 of thepresent invention may further comprise a second major surface 66opposite the first major surface 65, and facing in an oppositedirection. The conductor 72 passes completely through the body 60 andhas a second end 72 on or above the second major surface 66. The term“above,” as used herein, refers to a direction away from the body oneither side of the body, and is not necessarily related to theorientation of the body in space. The term “above” therefore refers tothe different directions on different sides of the body.

[0065] A second contact 90 is attached to the conductor 72 at its secondend 91. A second compliant layer 61 is formed on the second majorsurface 66, and the second contact 90 may be formed either on or abovethe surface 64 of the second compliant layer.

[0066] The interposer 50 of the invention is for making connections to acircuit board 80 (FIG. 2) having contact pads 81. The contact padsinclude a portion extending radially outwardly from a hole 83 in thecircuit panel. The contact pads may further include a portion formed byplating the hole 83 with a conductive material. An edge 84 is formed bythe contact pad at the periphery of the hole 83. In the contact padshown in FIG. 2, the edge 84 is formed at the juncture of the portion ofthe pad extending radially outwardly from the hole and the portionplated within the hole. The circuit panel 80 also includes circuitryinterconnecting the contact pads 81 with each other or with externalwiring.

[0067] A method of making a multilayer circuit according to theinvention using the interposer 50 is represented in FIGS. 2 and 3. Theinterposer is stacked with one or more circuit panels, such as circuitpanel 80, so that the first surface 65 of the interposer body confrontsa horizontally extensive surface 86 of the circuit panel. The compliantlayer 62 is on the first major surface 65 of the interposer body andlies between the body and the horizontally extensive surface 86 of thecircuit panel. The contacts 70 of the interposers confront the contactpads 81 on the circuit panel 80.

[0068] An additional circuit panel 92 may be stacked on the other sideof the interposer 50, with horizontally extensive surface 96 of thecircuit panel 92 confronting the second major surface 66 of theinterposer body. The compliant layer 61 is on the second major surface66 of the interposer body and lies between the body and the horizontallyextensive surface 96 of the circuit panel 92. The contacts 90 of theinterposer confront the contact pads 95.

[0069] The stacked panels and interposer are then compressed vertically,as shown in FIG. 3. The contacts 70, 90 are forcibly engaged with thecontact pads 81, 95 of the circuit panels. The contacts deform so thatthe central portions 75 of the contacts enter the holes 83 defined bythe contact pads. The peripheral portions 74 of the contacts havecircumferences larger than the diameter of the holes 83, so that theperipheral portions engage the contact pads 81, 95 around the holes. Asthe interposer 50 and the circuit panels 80, 92 are forced together, theperipheral portions 74 are forced vertically downward, toward the body60 of the interposer, wiping the contact pads. Wiping is concentrated atthe edges 84 of the holes.

[0070] The compliant layer 62 permits the peripheral portion 74 of thecontact to deform in a downward direction toward the body 60. Thecompliant layer 62 yields in response to the bending of the peripheralportion 74 toward the body 60.

[0071] As the contact 70 is forcibly engaged with the contact pad 81,frictional heat is developed, which, in a preferred embodiment,frictionally welds the contact to the contact pad. Such frictionalwelding creates highly reliable mechanical and electrical connectionsbetween the interposer and the circuit panel. Possible metallurgies ofthe contact and contact pad for use in this construction include, forexample, gold-gold, gold-tin, gold-tin-lead, tin-tin-lead, tin-tin,gold-copper and copper-copper.

[0072] The base 60 of the interposer 50 must be sufficiently flexible tocompensate for variations in planarity of the contact pads 81 of thecircuit panel. Where no compliant layer such as layer 62 is used, thebase must additionally be sufficiently deformable to permit deflectionof the peripheral portions of the contacts into the base material.Examples of possible base interposer materials include a polyimidebondply, a reinforced B-staged material, thermoplastic films andinsulated metal core materials.

[0073] In the embodiment of FIGS. 1-3, the layer 62 is a compliant layerthat is also an adhesive. The adhesive may be pressure-activatable, inwhich case the circuit panel 80 is bonded to the interposer 50 duringthe step of pressing those two elements together.

[0074] The adhesive may alternatively be a heat-activatable adhesive. Inthat case, the assembly is heated after the interposer and the circuitpanel are pressed together in order to activate the adhesive and bondthe two elements together.

[0075] As show in FIG. 3, where a two-sided interposer is used, thecircuit panel 80 and circuit panel 92 are electrically interconnected bythe through-conductor 72 after assembly. The contacts 70, 90 areintegral with the through conductor 72 and form a continuous electricalpath between the contact pads 81 and the contact pads 95 of the twocircuit panels. In a preferred embodiment, the through conductor, aswell as the hole in which it was formed, extends perpendicular to thefirst major surface 65 of the body 60 of the interposer.

[0076] The interposer 100 according to one embodiment of the inventionhas an array of contacts 70 arranged in a rectilinear grid, as shown inFIG. 4. Each of the contacts 70 has a non-circular periphery includingtabs 73. The tabs 73 are arranged in a symmetrical pattern about thecontact 70; in the embodiment shown in FIG. 4, four tabs are arranged ina quatrefoil pattern. The tabs 73 extend from a central portion of thecontact in a direction substantially diagonal to the rows and columns ofthe rectilinear grid.

[0077] In a presently preferred interposer according to the invention,the rectilinear grid of contacts 70 has a pitch 102 of approximately 1mm (0.040 inches) The pitch is measured between similar features ofadjacent contacts, such as a center-to-center distance. The interposerof the invention may be fabricated with pitches less than 1 mm in orderto accommodate microelectronic components having greater contactdensities. For example, an interposer having a contact grid array pitchof less than 1 mm is preferred; an interposer having a rectilinear arrayof contacts with a pitch of less than 0.75 mm (0.030 inches) is morepreferred. An interposer having a contact pitch of less than 0.5 mm(0.020 inches) is most preferred.

[0078] Features within a contact array require process resolutionconsiderably finer than the array pitch. For example, for an interposerhaving a contact pitch of 1 mm, holes in the circuit panels having adiameter of 0.4 mm (0.016 inches) are electroplated to 0.35 mm (0.014inches) to form the central holes of the contact pads. Holes in theinterposer having a diameter of 0.125 mm (0.005 inches) areelectroplated to 0.1 mm (0.004 inches) to form the through conductors ofthe interposer. Contact arrays having finer pitches requireproportionally smaller feature sizes and process resolutions.

[0079] A conductive bonding material 110 (FIG. 5) may be provided forbonding the contact 70 to the contact pad of the circuit panel. Theconductive bonding material may be a solder, a brazing alloy, a defusionbonding alloy, a polymer impregnated with conductive materials, oranother activatable conductive bonding material. While shown on thecontact 70 in the illustrative embodiment, the bonding material 110 mayinstead be present on the contact pad of the circuit panel, or may beapplied to both the contact 70 and the contact pad.

[0080] After compressing the interposer and the circuit panel so thatthe contact 70 is urged against a contact pad on the circuit panel, thebonding material 110 is activated to form an electrical and mechanicalbond between the contact pad and the contact. Typically, the bondingmaterial is activated by momentarily heating the assembly. In the caseof flowable bonding material such as solder, the bonding materialbecomes temporarily flowable and wets the contact and contact pad. Aftercooling, the contact material resolidifies, forming a bond.Alternatively, momentary heating of the bonding material may causechemical reactions, such as in the case of certain polymeric bondingmaterials and epoxy bonding materials.

[0081] The step of momentarily heating the assembly may not onlyactivate the bonding material 110 between the contacts 70 and thecontact pad of the circuit panel 10, but also activate the adhesivelayers 61, 62 (FIGS. 2-3), forming a unitary structure including theinterposer together with adjoining circuit panels. The step ofmomentarily heating the assembly may also soften the materialimmediately below the peripheral portion 74 of the contact (FIG. 3),permitting the contacts to deform downwardly toward the body 60 as wellas inwardly toward the conductor 72 when the peripheral portion 74 isengaged with a contact pad.

[0082] A gap 115 (FIG. 6) may be formed between the contact 70 and thefirst surface 65 of the interposer body 60. A similar gap 116 may beformed between the opposite surface 64 of the body 60, and a secondcontact 90. While the gaps are shown between the contacts and theinterposer body, similar gaps may be provided between the contacts andthe compliant or adhesive layers, where such layers are used. The gaps115, 116 provide clearance for deformation of the peripheral portions 74of the contacts 70, 90 upon engagement with contact pads on circuitpanels. By spacing the contacts above the surfaces of the interposerbody, contact between the contacts and facing contact pads on thecircuit panels is assured before the first surface 65 contacts thefacing surface of the circuit panel. Furthermore, the gap 115 permitsdeformation of the periphery 74 of the contacts 70 without requiring adeformable material beneath the contacts 70. Thus, the body 60 need notnecessarily be formed of a compressible or deformable material.

[0083] As the contact 70 deforms upon engagement with the contact pad81, the peripheral portion 74 (FIG. 7) moves in a downward direction 121toward the body 60 of the interposer, and in an inward direction 122toward the conductor 72. During this movement, the edge 84 of thecentral hole 83 in the contact pad 81 wipes along the surface of thecontact 70, breaking through oxidation layers to form a metal-to-metalcontact between the contact pad 81 and the contact 70. The wiping actionmay further induce friction welding or “cold” welding between those twocomponents, forming a permanent mechanical bond. If an adhesive or othercompliant layer 62 is present, that layer is deformed in the area aroundthe peripheral region of the contact, as the contact is deformeddownward and inward.

[0084] The substantially cylindrical conductor 72 is attached to thebody 60 of the interposer and has sufficient rigidity so as to remainsubstantially undeformed during the engagement process. Thus, a verticalposition 123 of the first end 71 of the conductor with respect to thefirst surface 65 of the interposer body remains substantially unchangedduring the engagement. The first end 71 of the conductor 72 therebyenters the hole 83, dragging the peripheral portion 74 of the contact 70across the edge 84 of the hole.

[0085] Where the contact 70 comprises a plurality of tabs such as tabs73 (FIG. 6), forces between the tabs and the edge 84 of the contact padhole are concentrated at the edges 125 of the tabs. The edges 125 of thetabs therefore wipe the edge 84 of the contact pad hole with relativelygreat force, removing oxide layers in that area and promoting coldwelding.

[0086] To prevent the conductor 72 from collapsing during engagement ofthe contacts 70 with the contact pads 81, the conductor 72 may have anincreased wall thickness as compared to the contact 70. Further, theclosed cylindrical shape of the conductor 72 creates a column-likestructure that is resistant to compressive forces during contactengagement. Other shapes known to be resistant to compressive columnloads, such as a triangular box beam, may be used.

[0087] The contact 70 may be formed directly on a primary surface 165 ofan interposer body 160 (FIG. 8). In that case, the interposer body 160must be deformable in order to permit the contacts 70 to deformdownwardly and inwardly upon engagement with opposing contact pads.While an entire interposer body may be fabricated from a uniformlycompliant material, such an approach is not practical with certainmaterials because of the strength requirement of the interposer in areasbetween contacts. Another solution is to provide a compliant region 168in the interposer 160 in a local area beneath the contact 70. Such aregion may be formed by using an initially b-staged material for formingthe body 160, then forming the contacts on the body and finally curingthe body 160 in all areas other than those beneath the contacts 170.Such selective curing may be done by radiation curing with a mask (notshown) blocking the areas around the contacts, or by using the contacts170 themselves as a mask during curing.

[0088] The thickness of an adhesive layer 162 (FIG. 9) may be increasedin the area surrounding the contact 70 in order to provide support forthe contact during transport and handling of the interposer. In thatcase, the compliant layer 162 comprises a region of smaller thickness164 in an area remote from contacts 70 and a region of increasedthickness 163 directly beneath the contacts 70. The region 163 providessupport for the contact during handling. The area of decreased thickness164 permits the contact 70 to contact the contact pads of the circuitpanel, and assure complete contact before the top surface of theadhesive or compliant layer 162 contacts the facing surface of thecircuit panel. Where no adhesive or other compliant layer is used, theinterposer body itself may have areas of reduced thickness in regionsbetween contacts. In either case, the regions of reduced thickness maybe formed using a plasma etching process, wherein the contact itselfacts as a mask, preventing etching of the material directly below.

[0089] Contact tabs 178 (FIG. 10) may be provided with asperities 179 ontheir upper surfaces in order to enhance wiping action between the tabsand the mating contact pads on the circuit panels. The asperities may beformed by selectively etching the top surfaces of the tabs. In analternative embodiment, the asperities may be provided on the facingsurfaces of the contact pads. In either case, the asperities breakthrough the oxidation layers on the opposing surfaces, formingmetal-to-metal contact.

[0090] The contacts of the present invention are highly tolerant of sizeand/or positional errors in the contacts themselves and in matingcontact pads. For example, as shown schematically in FIG. 11, a contact270 having tabs 273 may be used with a contact pad having a largehole-size tolerance, represented by circles 280, 281. The edge formed byeither hole 280, 281 is wiped by the four tabs 273 during engagement,removing oxidation and forming a metal-to-metal contact. Thus, contactengagement is not excessively affected by hole size.

[0091] Contact engagement according to the invention is also robust withregard to positional tolerances affecting the relative positions of thecontact and the corresponding contact pad. As shown in FIG. 12, acontact 270 having four tabs 273 may effectively engage contact padswith a wide range of positions, represented by holes 283-286. Whilepositional deviation will result in some tabs 273 being deformed to agreater degree than others in a single contact, the design permitsvariations in relative position without substantially affecting theoverall mechanical and electrical performance of the joint.

[0092] A contact pad 291 (FIG. 13A) of a circuit panel may have apolygonal hole, such as square hole 294. Such a hole presents multiplesurfaces for wiping the contact as it is inserted. A contact 292 (FIG.13B) having a circular periphery 295 may be used in conjunction with thesquare hole 294. A conductor connected to the central portion 293 has asufficiently small diameter to clear the square hole 294, givenpositional and size tolerances as illustrated in FIGS. 11 and 12.

[0093] The relative sizes of the periphery 295 of the contact and thesquare hole 294 of the contact pad 291 are selected so as to contact aplurality of substantially separate edge portions 296 (FIG. 13C) of thecontact 292. It is believed that the edge portions “fold” downward andinward as the contact and contact pad engage. That configuration permitsthe use of the circular periphery 295 without resulting in excessiveengagement forces. In contrast, full engagement around the periphery ofa circular contact does not permit “folding” of such edge portions, andthus results in high engagement forces. A circular contact periphery 295is desirable in the manufacture of smaller pitch sizes, because of thelimitations in the photolithographic process.

[0094] A tabbed contact 310 (FIG. 14) may also be used in conjunctionwith a polygonal hole 320 in a contact pad. For example, a contacthaving three tabs 312 may be inserted in a triangular hole 320 havingedges 322 forming vertices 321. In this case, the tabs 312 are alignedwith the vertices 321, forming two primary contact points 314 on eachtab 312 between the tab edges 313 and the edges 322 of the triangularhole. Localized contact at the contact points 314 results in highcontact stresses with increased wiping and increased cold welding.

[0095] In another aspect of the invention, the tabs 332 (FIG. 15) mayhave a circumferential width 341 near the tips that is greater than thecircumferential width 340 near the central portion 339. In that case,the contact points 334 between the tab edges 333 and the edges 342 ofthe contact pad hole 345 move along the contact pad hole edges 342 asthe contact is inserted into the hole. Such a configuration increasesthe total wiped area available for electrical and mechanical bonding.

[0096] The photolithographic process used in forming the contacts may beused to create a wide variety of contact geometries. For example, asshown in FIGS. 16A-16C, the number of tabs in a multiple-tabbedconfiguration may be reduced to form a three-tabbed contact 410, atwo-tabbed contact 412 or a one-tabbed contact 413. A reduced number oftabs requires less resolution in the photolithographic process bypermitting the formation of wider tabs, which are less likely to be lostduring imaging.

[0097] Star-shaped configurations, such as those shown in FIGS. 16D-16G,have points 415 on the tips of the tabs. Where the contact is completelypressed into the hole in the contact pad, the points 415 scrape theinside wall of the hole, improving the mechanical and electricalconnection. The scraping of the tips of the tabs within a contact padhole may be enhanced by providing multiple points 416 (FIG. 16H) on thetabs. Furthermore, the relatively large number of tabs in a star-shapedconfiguration provide multiple conductive pathways between the contactand the contact pad. Such multiple pathways make the joints lesssensitive to the loss of tabs in the photolithographic process, as wellto defective joints between a tab and the mating contact pad.

[0098] A contact 420 (FIG. 16I) having a large number of tabs provides alarge number of electrical paths between the contact and the contactpad. Such a contact may form a substantially continuous conical shapeupon insertion into a contact pad hole, providing the maximumcross-sectional conductive area between the interposer and the circuitpanel.

[0099] In a process for forming an interposer according to theinvention, an initial laminate is first formed. A polyimide body 560(FIG. 17A) is first coated with a compliant adhesive 561, 562. Theadhesive may be a thermoplastic or b-staged adhesive, and is preferablya thermoplastic. In a most preferred embodiment, the adhesive isselected from the group consisting of polyetherimide (PEI) andpolyimide. In the preferred embodiment shown, the adhesive is applied toboth surfaces of the body 560. The adhesive may be applied by transferlamination, or by mechanically or chemically coating the polyimide sheetwith a layer of adhesive.

[0100] Sacrificial metallic layers 550, 551 are next applied to theexposed surfaces of the adhesive. The metallic layers are formed of amaterial selected to be chemically removable without removing thecontacts and conductors formed later in the process. For example, apreferred sacrificial layer material is aluminum.

[0101] Through holes 565 (FIG. 17B) are next formed in the resultinglaminate. The through holes may be drilled, such as by laser ablation,or may be punched or otherwise formed in the laminate. The holes extendcompletely through the base layer 560, the adhesive layers 561, 562 andthe sacrificial layers 550, 551.

[0102] The entire assembly is next sputter metalized to form a flashmetallic layer 567 (FIG. 17C). The flash metallic layer 567 ispreferably gold, but may alternatively be tin, copper or another metalcompatible with the materials used in the contact and conductor-formingprocesses. The metalization process forms a layer on the exposedsurfaces of the sacrificial layer 550, 551, as well as within the holes565.

[0103] The contacts 570 and conductors 572 (FIG. 17D) are next formed inthe holes. The contacts and conductors are preferably formed integrallyby first forming patterned photoresist layers (not shown) defining theouter periphery of the contacts on the flash coated outer surfaces ofthe sacrificial layers 550, 551. The contacts 570, 572 are then formedby electroplating the contact material onto the areas not covered withphotoresist. The contact material is then plated with a gold or tinfinish layer 575, and the photoresist pattern layers are removed.

[0104] The sacrificial aluminum layers 550, 551 are then removed usingan etchant that leaves the contacts 570 and conductors 572 substantiallyintact. The removal of the sacrificial layers leaves a gap 515 betweenthe contact 570 and the adhesive layer 562. That gap permits deformationof the contact 570 upon engagement with a contact pad on a matingcircuit panel. Because the contacts 570 are spaced away from the outersurface of the adhesive 562, full engagement of the contacts withcontact pads is assured before engagement of the adhesive 562 with thefacing surface of the circuit panel.

[0105] The above method of fabricating an interposer according to theinvention may be performed without applying a sacrificial layer on theadhesive. In that case, the contacts are formed directly over theadhesive layer. The adhesive layer is formed of a material selected tobe compliant in order to permit the contact 570 to deflect downward andinward into the adhesive layer. Furthermore, while the method wasdescribed as including an adhesive layer, that layer may be replaced byanother compliant layer that does not necessarily adhere to the circuitpanel. Furthermore, the compliant layer or adhesive layer may becompletely eliminated, either forming the contact 570 spaced away fromthe body 560 to permit deformation, or using an at least locallycompliant body 560 to permit deformation of the contacts into the body.

[0106] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An interposer for making connections to electrical contact pads on asurface of a microelectronic element defining holes therein, theinterposer comprising: (a) a body having a first major surface, saidbody having horizontal directions parallel to said first major surface,and vertical directions perpendicular to said first major surface; (b) aplurality of conductors in said body; and (c) a plurality of contacts onor above said first major surface, each said contact being permanentlyjoined to one said conductor and extending radially outwardly from theconductor, each said contact having a periphery remote from theconductor and a central portion attached to the conductor; each saidcontact being adapted to deform so that the periphery of the contactwill contract radially inwardly toward the central portion of thecontact in response to urging said periphery of the contact against acontact pad and inserting the central portion of the contact into thehole defined by the contact pad; whereby said contacts will wipe thecontact pads of the microelectronic element when the microelectronicelement is juxtaposed with said first surface and forced toward saidbody.
 2. An interposer as claimed in claim 1 , wherein each said contactbends vertically downwardly so that the periphery of the contact movestowards the body, as well as contracting radially inwardly toward thecentral portion of the contact.
 3. An interposer as claimed in claim 2 ,wherein the periphery of each said contact is spaced vertically abovesaid body, with a gap between the periphery of said contact and saidbody.
 4. An interposer as claimed in claim 2 , wherein said body isdeformable at least near the periphery of each said contact, wherebysaid movement of said periphery toward said body causes said peripheryto engage and deform said body.
 5. An interposer as claimed in claim 2 ,wherein said body further comprises an adhesive layer on said firstmajor surface for adhering said interposer to said microelectronicelement.
 6. An interposer as claimed in claim 5 , wherein said contactsare disposed on said adhesive layer.
 7. An interposer as claimed inclaim 6 , wherein said adhesive layer has a thickness beneath saidcontacts greater than a thickness of said adhesive layer between saidcontacts.
 8. An interposer as claimed in claim 1 , wherein the peripheryof each said contact is noncircular.
 9. An interposer as claimed inclaim 8 , wherein each said contact includes a plurality of tabsextending radially outwardly away from the conductor, each said tabhaving a tip remote from the conductor.
 10. An interposer as claimed inclaim 9 , wherein said tabs of each said contact are disposed in asubstantially symmetrical pattern about the juncture of the contact andthe associated conductor.
 11. An interposer as claimed in claim 10 ,wherein each said contact includes four said tabs, and saidsubstantially symmetrical pattern is a quatrefoil pattern.
 12. Aninterposer as claimed in claim 11 , wherein said contacts are disposedin a substantially rectilinear grid having rows and columns, and whereinsaid tabs extend substantially diagonally with respect to said rows andcolumns.
 13. An interposer as claimed in claim 9 , wherein said tabs aredisposed in a star pattern with tips of said tabs having acircumferential width less than a circumferential width of said tabsnear said central portion.
 14. An interposer as claimed in claim 9 ,wherein a circumferential width of said tabs near said tips is greaterthan a circumferential width of said tabs near said central portion. 15.An interposer as claimed in claim 1 , wherein each said contact includesa conductive bonding material adapted to facilitate electrical joiningof said tabs to contact pads engaged therewith.
 16. An interposer asclaimed in claim 15 , wherein said conductive bonding material isselected from the group consisting of solders, brazing alloys, diffusionbonding alloys and conductive materials incorporating a polymer.
 17. Aninterposer as claimed in claim 1 , wherein each said contact is formedintegrally with the associated conductor.
 18. An interposer as claimedin claim 17 , wherein each said conductor extends substantiallyperpendicularly to said first surface.
 19. An interposer as claimed inclaim 1 , wherein said conductors are arranged at a pitch of less thanabout 1.0 mm, from center to center.
 20. An interposer as claimed inclaim 1 , wherein said body defines a second major surface facing in anopposite direction from said first major surface, at least some of saidconductors being through conductors having first ends disposed adjacentsaid first major surface and second ends disposed adjacent said secondmajor surface, at least some of said contacts being permanently joinedto said first ends of said through conductors, the interposer furtherincluding second-end contacts on or above said second major surfacepermanently joined to said second ends of said through conductors; eachsaid second-end contact extending radially outwardly from the associatedconductor, each said second-end contact having a periphery remote fromthe conductor; each said second-end contact being adapted to deform sothat the periphery of the contact will contract radially inwardly towardthe central portion of the contact in response to urging said peripheryof the contact against a contact pad of a second microelectronic elementand inserting the central portion of the contact into a hole defined bythe contact pad; whereby said contacts will wipe the contact pads of thesecond microelectronic element when the second microelectronic elementis juxtaposed with said second surface and forced toward said body. 21.An interposer for making connections to pads on the surface of amicroelectronic element, said pads defining holes therein, comprising:(a) an interposer body having a first surface; and (b) a plurality ofcontacts on said body, each said contact comprising a central portionextending through said first surface into said body, and a peripheralportion extending radially from said central portion on or above saidfirst surface, said peripheral portion of each said contact beingadapted to bend downward, toward said body, and said central portionadapted to remain substantially undeformed, in response to a force onsaid peripheral portion directed downwardly toward said body.
 22. Aninterposer as claimed in claim 21 , wherein said central portion issubstantially cylindrical.
 23. An interposer as claimed in claim 21 ,wherein said peripheral portion comprises a plurality of tabs extendingradially from said central portion.
 24. An interposer as claimed inclaim 21 , further comprising a deformable layer between said firstsurface and said peripheral portions of said contacts.
 25. An interposeras claimed in claim 24 , wherein said deformable layer is an adhesivelayer.
 26. An interposer as claimed in claim 21 , wherein saidperipheral portion and said first surface define a gap therebetween. 27.An interposer for making connections to electrical contact pads on asurface of a microelectronic element, the interposer comprising: (a) aninterposer body having a first surface; and (b) a plurality of contactson said body, each said contact including a central portion and aplurality of tabs extending radially outwardly from the central portion,all of said tabs extending over said first surface, each said tab beingadapted to deform radially inwardly, toward the central portion, inresponse to a force on such tab directed downwardly toward said body.28. An interposer as claimed in claim 27 , in which the tabs of saidcontacts have top surfaces facing upwardly away from said body andasperities on such top surfaces, whereby said asperities will engage andwipe a contact pad engaged with the contact.
 29. A method of making amicroelectronic interposer comprising the steps of: (a) providing a bodydefining a first surface; (b) providing a first temporary layer oversaid first surface; (c) forming apertures passing through said body andsaid temporary layer; (d) depositing a layer of an electricallyconductive structural material in each said aperture and over saidtemporary layer proximate said aperture to thereby form contacts; and(e) removing said temporary layer, leaving said contacts with outwardlyflaring peripheral portions spaced vertically above said first surfaceof said body.
 30. A method as claimed in claim 29 , further comprisingthe step of depositing a first layer of adhesive on said first surfaceof said body before providing said first temporary layer, said temporarylayer being provided over said adhesive layer, whereby said adhesivelayer is left exposed after said step of removing said temporary layer.31. A method as claimed in claim 30 , wherein said adhesive layer isformed from an adhesive selected from the group consisting ofthermoplastic adhesives and b-staged adhesives.
 32. A method as claimedin claim 30 , wherein said adhesive layer is formed from a thermoplasticselected from the group consisting of polyimide and polyetherimide. 33.A method as claimed in claim 29 , wherein said temporary layer is formedfrom a metal selected from the group consisting of aluminum, tin, andnickel.
 34. A method as claimed in claim 29 , wherein said body furtherdefines a second surface opposite said first surface; said methodfurther comprising the step of providing a second temporary layer oversaid second surface; said apertures passing through said secondtemporary layer; and said deposited structural material extends oversaid second temporary layer proximate said apertures to thereby formsecond contacts.
 35. A method of making a microelectronic interposercomprising the steps of: (a) providing a body defining a first surface;(b) providing a first compliant layer over said first surface; (c)forming apertures passing through said body and said compliant layer;(d) depositing a layer of an electrically conductive structural materialin each said aperture and over said compliant layer proximate saidaperture to thereby form contacts with outwardly flaring peripheralportions on said compliant layer.
 36. A method as claimed in claim 35 ,wherein said compliant layer comprises an adhesive.
 37. A method asclaimed in claim 35 , further comprising partially etching saidcompliant layer whereby said compliant layer has a thickness under saidcontacts greater than a thickness between said contacts.
 38. A circuitassembly comprising an interposer and a circuit panel having contactpads defining holes, a first surface of said interposer confronting asurface of said panel, said interposer having a body defining said firstsurface and conductors having ends adjacent or above said first surfaceand having a contact at each said conductor end, each said contactincluding a peripheral portion extending generally horizontally from theassociated conductor end, said peripheral portions of said contactsconfronting the contact pads on the circuit panel facing saidinterposer, said conductor ends received within said holes defined bysaid contact pads, said peripheral portions of said contacts beingengaged with said contact pads whereby the peripheral portion of eachcontact has contracted radially inwardly toward the associated conductorend so that each said peripheral portion has moved horizontally withrespect to the engaged contact pad and has wiped said contact pad.
 39. Acircuit assembly comprising an interposer having a plurality ofelectrically conductive contacts on a first surface thereof, a circuitpanel having contact pads defining holes, said circuit panel and saidinterposer stacked in vertically superposed arrangement so that a firsthorizontally-extensive surface of said interposer confronts a firsthorizontally-extensive surface of the circuit panel and so that aplurality of electrically conductive contacts on said first surface ofsaid interposer confront the contact pads on the circuit panel facingsaid interposer forming a stacked panel; and said stacked panel beingvertically compressed so as to forcibly engage said contacts with saidcontact pads whereby said contacts are deformed so that at least aportion of each contact is received within a hole defined by one of saidcontact pads and at least a portion of each contact engaged with acontact pad has moved horizontally inward and vertically downward withrespect to the first surface of the interposer for wiping the contactpad.
 40. A multilayer circuit assembly comprising at least oneinterposer having a body defining first and second surfaces, saidinterposer including a plurality of conductors each having a conductorend adjacent or above said first surface and having a contact at eachsaid conductor end, each said contact including a peripheral portionextending generally horizontally from the associated conductor end; atleast one circuit panel having contact pads defining holes therein; saidcircuit panel and said interposer being stacked so that said firstsurface of said interposer confronts a surface of said panel and saidperipheral portions of said contacts confront said contact pads on thecircuit panel facing said interposer; and said circuit panel and saidinterposer compressed together such that said conductor ends haveentered said holes defined by said contact pads, and said peripheralportions of said contacts have forcibly engaged said contact padswhereby said peripheral portion of each contact has contracted radiallyinwardly toward the associated conductor end so that each saidperipheral portion has moved horizontally with respect to the engagedcontact pad for wiping said contact pad.